Silencing of a metaphase I-specific gene results in a phenotype similar to that of the Pairing homeologous 1 (Ph1) gene mutations

• Published in: Proceedings of the National Academy of Sciences - PNAS 2014-09, Vol.111 (39), p.14187-14192
• Main Authors: Bhullar, Ramanjot, Nagarajan, Ragupathi, Bennypaul, Harvinder, Sidhu, Gaganpreet K., Sidhu, Gaganjot, Rustgi, Sachin, von Wettstein, Diter, Gill, Kulvinder S.
• Format: Article
• Language: English
• Subjects: Alternative Splicing; Arabidopsis; Arabidopsis - genetics; Base Sequence; Biological Sciences; Centromeres; Chromosome pairing; Chromosome Pairing - genetics; Chromosomes; Chromosomes, Plant - genetics; Conserved Sequence; Deoxyribonucleic acid; Department stores; Diploidy; DNA; DNA, Plant - genetics; Exons; Gene Deletion; Gene expression; Gene Silencing; Genes; Genes, Plant; introgression; Meiosis; metaphase; Metaphase - genetics; Models, Molecular; Mutation; new species; Oryza - genetics; Phenotype; Phenotypes; Plant Proteins - chemistry; Plant Proteins - genetics; Plants; Plants, Genetically Modified; Polyploidy; Protein Conformation; Proteins; Transcriptome; Triticum - cytology; Triticum - genetics; Triticum aestivum; Wheat
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1416241111

Significance Maintaining diploid-like pairing behavior is essential for a polyploid to establish as a new species. The Pairing homeologous 1 ( Ph1 ) gene, regulating such behavior in polyploid wheat, was identified in 1958, but its molecular function remained elusive. The present communication reports identification of the candidate Ph1 ( C-Ph1 ) gene that is expressed exclusively during meiotic metaphase I, whose silencing resulted in formation of multivalents like the Ph1 gene mutations. Although the C-Ph1 gene has three homoeologous copies, the 5B copy has diverged in sequence from the other two copies. Heterologous gene silencing of the Arabidopsis homologue of the C-Ph1 gene also confirmed its function. Molecular characterization of this gene will make it possible to develop precise alien introgression strategies. Although studied extensively since 1958, the molecular mode of action of the Pairing homeologous 1 ( Ph1 ) gene is still unknown. In polyploid wheat, the diploid-like chromosome pairing is principally controlled by the Ph1 gene via preventing homeologous chromosome pairing (HECP). Here, we report a candidate Ph1 gene ( C-Ph1 ) present in the Ph1 locus, transient as well as stable silencing of which resulted in a phenotype characteristic of the Ph1 gene mutants, including HECP, multivalent formation, and disrupted chromosome alignment on the metaphase I (MI) plate. Despite a highly conserved DNA sequence, the C-Ph1 gene homeologues showed a dramatically different structure and expression pattern, with only the 5B copy showing MI-specific expression, further supporting our claim for the Ph1 gene. In agreement with the previous reports about the Ph1 gene, the predicted protein of the 5A copy of the C-Ph1 gene is truncated, and thus perhaps less effective. The 5D copy is expressed around the onset of meiosis; thus, it may function during the earlier stages of chromosome pairing. Along with alternate splicing, the predicted protein of the 5B copy is different from the protein of the other two copies because of an insertion. These structural and expression differences among the homeologues concurred with the previous observations about Ph1 gene function. Stable RNAi silencing of the wheat gene in Arabidopsis showed multivalents and centromere clustering during meiosis I.